二维晶体及其界面异质结中超导等量子态的研究和调控

Superconductivity is a hot research topic which has long history while the application-leading R&D based on it also has very attractive prospect. Presently, the most important question for superconductivity research is to unveil the superconductivity mechanism hence to increase the superconductivity critical transition temperature. According to historical research experience, people found that high superconducting transition temperature was usually discovered in the materials which has (quasi) two dimensional(2D) structure and two coexisting ordered ground states. However, the mechanism is still not clear. Therefore, considering the present worldwide research status, investigating and tuning the many-body states in 2D crystals and their hetero-structures is selected as the topic of present project, aiming for seeking higher superconducting transition temperature and revealing the mechanism of high temperature superconductivity. Based on applicant’s experience on superconductivity and 2D material device, we will grow high quality 2D single crystals and their hybrid structures by chemical vapour deposition(CVD), fabricate devices by micro-processing technique. By exploiting methods of ion gel gating, hetero structure tuning etc, we will investigate the properties of 2D superconductivity, including symmetry of the Cooperpair wavefunction, the factors that determining the transition temperature, such as impurity, disorder, other ordered states, etc and the details of the phase diagram of superconductivity insulator/metal transition. Meanwhile, we will also investigate the candidate materials for the application of superconducting nanowire single photo detector(SNSPD).

超导是凝聚态物理的明珠，经久不衰，同时基于超导的应用研发也有着极为诱人的前景。当前，对超导研究的一个最重要的问题是弄清楚超导的机理并提高超导临界转变温度。根据历史研究经验，人们发现（准）二维和有多个低温有序态的超导体系具有较高的超导转变温度，但其机理尚未清楚。因此，结合国内外研究现状，本项目选题为对二维晶体及其界面异质结中超导等多体量子态的研究和调控，以寻找更高的超导转变温度，揭示高温超导机理为目标。拟利用申请人在超导和二维材料器件两个领域的丰富研究经历，通过化学气相沉积等手段制备高质量的二维晶体及其异质结材料，通过微加工制备微纳器件，利用离子液体栅极调控，界面异质材料调控等方法，进一步研究二维超导体系的性质，包括二维超导的波函数配对性质，临界转变温度的影响因素，如杂质，无序，其它有序态等的影响以及超导绝缘体/金属转变的相图细节等，同时进行其基于超导纳米线单光子探测应用的探索。

该项目是在几年前二维材料领域的研究人员在对半导体等二维材料做了比较充分研究，开始转向对关联电子二维材料研究的时候进行立项，该项目的目标是要厘清二维材料中的多体量子态，如比较常见的电荷密度波态和超导态等，也包括铁磁，铁电态，的产生机制，维度降低产生的新特性，以及其操控方式，为开发可应用的器件做前期偏基础的研究。主要研究内容是对不同维度的电荷密度波和超导材料的光，电，磁等性质进行测试，发现新规律，新特性，发掘新应用。我们通过该项目的经费支持，取得了以下成果：1我们对准一维电荷密度波材料TaSe4I0.5做了仔细的光电探测研究，发现基于其260K以下的电荷密度波态到正常态的几个数量级的电导变化，可以实现从可见到中红外的宽波段，高光电响应度和高探测率的光电探测（405 A/W @ 532 nm；31.67 A/W @ 4.73 um；7.2×109 Jones @ 532 nm, 5.6×108 Jones @ 4.73 um），该双高的光电探测性能尤其在中红外非常重要，因为比商用的工作在液氮温度的HgCdTe材料的性能还要好。我们发现，只有在准一维的电荷密度波体系中，有Luttinger Liquid到电荷密度波的相变才拥有这样高的光电探测表现。论文正在投稿；2发现在电荷密度波态和超导态共存的体系，二维1T-TiSe2中，真正零电阻的超导基态并不存在，这印证了二维超导态很强的量子涨落以及在超导和电荷密度波两种量子基态共存区域增强的量子涨落的共同影响；同时发现随外磁场增强，量子金属态随磁场的演化分为玻色金属和磁通量子蠕动两个阶段，这一发现，丰富了量子金属态的物理图像，该工作已于2019年在Nano Letters发表。